This invention relates to a connector for coiled tubing and more particularly to an end connector for composite coiled tubing to adapt the composite coiled tubing to be connected to various types of apparatus or equipment used in downhole operations in a wellbore.
Reeled or coiled tubing has been run into wells for many years for performing certain downhole operations, including, but not limited to, washing out sand bridges, circulating treating fluid, setting downhole tools, cleaning the internal walls of well pipes, conducting production fluids or lift gas, and a number of other similar remedial or production operations.
Conventionally, coiled tubing is made of steel. Although steel has been and is useful in such downhole operations, other materials are available which provide certain advantages over steel coiled tubing. For instance, coiled tubing may be made from a nonferrous material which will not suffer from some of the structural limitations of steel tubing and which is more resistant to chemicals. Coiled tubing may thus be made from fibrous composite material which results in a composite coiled tubing that is not as heavy as steel coiled tubing, provides greater corrosion resistance and has a longer fatigue life.
Such composite coiled tubing used in wellbore operations may be exposed to external pressures in excess of 5000 psi, and internal pressures as high as 15,000 psi. Tension and compression forces caused by the tubing being forced into or pulled out of a wellbore may exceed 60,000 lbf.
In order to perform the various wellbore operations, it is usually necessary to make connections between the composite coiled tubing and different types of apparatus or equipment used in downhole operations. The connection must be capable of handling the severe loads and pressures experienced during such operations. Numerous known connectors and connecting techniques, such as welding, are utilized with steel coiled tubing. Welding is not an option with composite coiled tubing and steel tubing connectors, like that described in U.S. Pat. No. 4,936,618 to Sampas et al., are not applicable to the composite coiled tubing being developed for use in downhole operations.
One type of end connector for use with composite coiled tubing is disclosed in application Ser. No. PCT/US96/15427. The connector shown there includes a load collar and housing arrangement disposed about the outer surface of the composite coiled tubing. Although the connector shown therein may provide an adequate structural connection capable of handling the extreme conditions that may exist in a wellbore, there are circumstances when such a connector cannot be used. For example, there may be circumstances where it is desirable to use composite coiled tubing in downhole operations where the inner diameter of the casing, production tubulars, or other downhole apparatus through which the tubing must pass, is such that a connector having a diameter greater than the tubing would cause an unacceptable amount of interference as the tubing is lowered into or raised from the wellbore. Similar difficulties may not occur with respect to steel coiled tubing, since steel tubing typically will have a thinner wall than composite coiled tubing connector.
This invention resolves any such difficulty by providing an end connector having an outer surface that is substantially flush with the outer surface of the composite coiled tubing when connected thereto, so that composite coiled tubing can be used in virtually any wellbore for which steel coiled tubing having the same inner diameter would be used, without causing any interference problems with the inner walls of the casing or production tubulars.